ABS problem, 87 300D - PeachParts Mercedes-Benz Forum

awsrock · #1 10-21-2008, 11:28 PM

So I might consider tackling my ABS problem this weekend, since it is going to be getting cold and snowy soon.

In my searches, it seems like I might have a bad pump
The symptom is that once I begin driving, the brakes pulsate, sort of oddly, with a very firm pedal, on the first and sometimes second use, and after that the ABS light goes on and then the brakes operate normally. I have a new OVP in there, so that is not the culprit. Based on something Babymog said, it sounds like it is the pump-
"When you power up, the ABS light comes on with the rest. normal
After a few seconds, the ABS light goes out, normal.
When you first start to drive, the ABS pump cycles, self-test, about 5mph, normal.
If the light doesn't go out, bad sensor or other failure in the initial power-up test.
If the light comes on after the ~5mph self-test, pump or other failure."

Brain or sensors, perhaps? I could see those being problems, but this pulsating seems like there is something wrong too...not the normal ABS pulsating. I don't know how is should be though, as it has been broken since I got it this summer.

Is changing the pump difficult? It seems like I would just drain the fluid and swap them. There are a bunch on ebay for $25-30 so I was thinking of just getting another one and swapping it in.

Jeremy5848 · #2 10-22-2008, 12:38 AM

Mercedes dealers, and some indys, have a test gadget that will tell you what is wrong with your ABS. It might be worth spending a few bucks to have the tests performed. If you have a friendly mechanic who will do it for free, so much the better. You can then replace whatever the test says is the problem.

Replacing the pump should be as easy as you say. A pressure bleeder is very helpful and perhaps might even be considered mandatory to do a good job bleeding ABS-type brakes. I built my own for a few dollars and it was well worth it.

Jeremy

awsrock · #3 10-22-2008, 10:48 AM

I'll look into getting it checked out.

What is the function of the relay that is inside the ABS pump? Would a failure of that relay cause the pump to malfuntion / act weird?

babymog · #4 10-22-2008, 04:23 PM

If you have any reason to come around the lake, I have a spare system pulled from one of my ex-drivers, we can swap things around.

awsrock · #5 10-22-2008, 04:39 PM

Ahh, I'm actually going to be in Chicago for the weekend too! But you're still another 3 hours away...
Thanks for the offer, one of these days I'll probably be in the area. Don't think I'll be able to swing it this time, though.

awsrock · #6 10-27-2008, 08:32 PM

So, I haven't taken it in to get the ABS checked out, but things are changing...

I got a new serpentine belt tension spring this weekend after the old one broke, and that combined with the use of the heater has caused the ABS to seem to work most of the time (light staying off)...
However, when I turn off the heat (on economy), the light comes on after a little while.
Is it possible that the ABS was not getting enough voltage, and now with a new spring the alternator is working better? I never felt that it wasn't doing its job in the past. Would using the economy setting put more strain on the alternator making it produce more voltage? I don't understand the ACC symptom because this did not happen whenever I used it in the past. Perhaps the ABS computer is acting up?

JimmyL · #7 10-27-2008, 08:45 PM

Quote:

Originally Posted by awsrock

So, I haven't taken it in to get the ABS checked out.........

Stop right there. I think I see the problem......

awsrock · #8 11-09-2008, 05:58 PM

Problem solved:

Front wheel sensors were full of metal shavings and crud.
Front passenger wire looks like it might be in need of replacement soon, but for now it is working! No more ABS light.
I thought it was going to be something more serious than that, but I was wrong...which is fine because this was free!